Method of preparing phosphine



Nov. 5, 1963 1. GORDON METHOD oF PREPARING PHosPHINE Filed July 27, 1960 s r if@ 6 9 l O 9 r nr 3 3 I NUwI V fU//f n4/ur) 2*. :Inu

UnitedStates Patent O 3,169,793 METHUD F PREPARING PHSPHNE Irving Gordon, Niagara Fails, N.Y., assigner to Hooker Chemical Corporation, Niagara Fails, NX., a corporation of New York Filed .luly 27, 196i), Ser. No. 45,666 12 Claims. (Cl. MP4- 101) This invention relates to the preparation of phosphine by the electrolysis of phosphorous.

Heretofore, phosphine has been prepared by the reaction of metallic phosphides or phosphonium halides with Water, and by the hydrolysis of elemental phosphorous.

These methods have been unsatisfactory because of the high production costs and/ or because the phosphine product is in an impure form.

United States Patent No. 1,375,819, issued April 26, 1921, to Henry Blumenberg, Jr., discloses a method for preparing arsine by the electrolysis of a salt or oxide of arsenic in the presence of sulfuric acid and potassium sulfate or other compounds capable of liberating nascent hydrogen upon electrolysis. However, phosphine is not produced under the conditions set forth by Blemenberg when an oxide or salt of phosphorous is employed.

W. R. Grove, in the Journal of the Chemical Society, vol. i6 (1863), pp. 263-272, discloses the use of yan electric current to boil moist molten phosphorous and produces phosphine thereby. Such a technique requires a high voltage, and converts only a small amount of phosphorus to phosphine.

It is an object of this invention to provide a method of producing phosphine by electrolytic means.

Another object of the invention is to provide a more economical method of producing phosphine.

Still another object of the invention is to provide a method of producing phosphine in a form substantially free from lower phosphorus hydrides and other phosphorus impurities.

These `and other objects of the invention will be apparent from the following detailed description ofthe invention.

It has now been discovered that phosphine can be prepared by passing an electric current between an anode and a liquid cathode in contact with an electrolyte, the cathode also being in agitated contact with molten phosphorus, Suliicient agitation should be provided for the liquid cathode and molten phosphorus to permit the current to how between the cathode and the anode.

The accompanying drawing is a schematic illustration of a suitable electrolytic cell for carrying out the novel process. `Referring to the drawing, there is shown cell vessel `10, having a cathode section 11, and an anode section "12, the sections being separated by .a porous diaphragm 13. A gas-tight anode section cover 14 having ports l5', 16 and 17, is secured to the top of the cell vessel l0.

Extending through port is anode 1S, which is positioned in `anode section 12. Anode 13 is shown in the drawing as a cylinder, but any suitable shape may be employed. Cathode section 11 extendsthrough port 16 into anode section 12. to a point adjacent to, but removed from the bottom of cell vessel 10. A gas-tight cathode section cover 38 having ports 19, Ztl, 21, 22 and 23 is secured to the top of the cathode section .11. A liquid cathode 24 is placed in the bottom of cathode section 11,` up to the level indicated by interface 25. Molten phosporus 26 is placed in the cathode section `11 up to the level indicated by interface `27. An aqueous elecrolyte 28 fills the anode and cathode sections up to the level indicated by interface 29.

Cathode conductor 3l) which is covered with a suitable insulating material 39, such as glass, extends from molten 3,199,793- Patented Nov. 5, 1S63 ICC cathode 24 through port 19 to the negative pole of a source of electrical energy y31. Electric conductor 32 connects anode 1S with the positive pole of electrical energy source 31.

Motor driven agitation means 33 extends through port 20 into the liquid cathode. This type of agitating means is shown to demonstrate the preferred means for agitating the liquid cathode Iand molten phosphorus `in `a cell of this design, but any siutable type of agitating means may be employed.

When an electric current is passed between the cathode and the anode, a gaseous mixture comprised of phosphine and hydrogen is dicharged at the cathode and passes out the cathode section through catholyte gas discharge outlet 34, which extends to the exterior of the cell through port Z1. The gas produced in the anode section passes out through anolyte gas discharge outlet 35, which extends through port 17.

Funnel 36, which extends through port 23', 4is provided for the addition of electrolyte and/ or molten phosphorus to the cathode section 11.

A thermometer 37, or other suitable temperature measur-ing means, extends through port 22 into the electrolyte contained in cathode section 11.

It will be recognized by those skilled in the art that the design of the electrolytic cell shown in the drawing can be modified without departing from the spirit of the invention. For example, the position of the anode section and the cathode section can be reversed, -wherein liquid cathode and molten phosphorus are placed in the bottom of the cell vessel 10. In such a cell, the agitating means 33 is positioned in the bottom of cell vessel 10.

Regardless of the type of cell employed, it is important that suilicient agitation be imparted to the liquid cathode and the molten phosphorus to permit the llow of current between the cathode and the anode.

Cell vessel 10 may be constructed of glass, ceramics, rubber-lined steel, or other suitable impervious materials.

Porous diaphragm 13 may be construed of porous alundum, sintered glass, plastic cloth, glass cloth, or other porous materials, such as ion-exchange mebranes and the like.

Molten white phosporous, sometimes referred to as yellow phosphorus, is preferably employed as the source of phosporus for the phosphne product, but other allotropic forms of phosphorus may be employed if desired. The temperature of the phospohorus should be sufficient to maintain it in a molten state, without effecting boiling thereof. For this reason, the temperature of the molten phosphorus and electrolyte is maintained within the range between about forty-four degrees and about two hundred and eighty degrees centigrade, and preferably between about lifty and about one hundred and tweny degrees centigrade. Temperature control of the phosphorus and the electrolyte -is readily obtained by means of a constant temperature bath (not shown in the drawing), but any suitable temperature control means may be employed. For example, on startup of the electrolytic process, the molten phosphorus and electrolyte may be heated to a temperature within the aforesaid temperature range by means of anexternal source of heat, and maintained at this temperature by means of a constant temperature bath.

Any cathodic material which is liquid under the aforesaid conditions may be employed as a cathode in the Vdium phosphate, d-isodium phosphate, monopotassium phosphate, dipotassium phosphate, and mixtures thereof.

yAn aqueous phosphoric acid solution containing between ,about ten and about eighty, and preferably between about fifteen and about fifty percent phosphoric acid by weight, is preferably employed as the electrolyte, but other concentrationsV may be employed if desired. Concentration of the aqueous solutions of the aforesaid acids, when employed as an electrolyte, should be equivalent to the aforesaid phosphoric acid concentrations. Aqueous solutions of the Vaforesaid salts having a concentration between about ten percent by weight and the concentration suf- Alicient to produce' a'saturated solution underrthe temperature conditions obtained, may be used.

If phosphoric acid, sulfuric acid, or salts of these acids are employed as the electrolyte, the anolyte gas predominates in oxygen, when other than graphite is employed as the anode. tlf those acids and/or salts are employed as the electrolyte, and the anode is constructedfof graphite, the anolyte gas will predominate in carbon dioxide.

Control of the curnent and current density during electrolysis is important. The current should bemaintained at at least one ampere or above, preferably as high as possible without increasing the voltage above Yabout twenty volts. Current density is preferably maintained as high as possible, consistent with a reasonable level of phosphine production. phine production rates can be attained when the cath- .odic'current density is maintained at at least about live `am'peres per square foot and preferably between about ten and about seven hundred amperes per square foot. However, it will be recognized by those skilled in the art that optimum current and optimum current density will Vary with the particular cell design employed.

Y The gas produced at the'cathode in accordance with the instant novel process is a mixture of phosphine and hydrogen, containing as high as ninety percent phosphine or higher. When an acid is fused as the electrolyte, the

resulting catholyte gasV is substantially free from phosphorus hydride impurities, As a result when the catholyte gas is employed as a chem-ical intermediate, the

rproduct of the reaction is in a highly pure form. For

example, tetra-Itis(,hydroxymethyl) phosphonium chloride is prepared by the reaction of phosphine, formaldehyde, and concentrated hydrochloric acid. When phopshline prepared by the conventional process is employedV to produce tetralds(hydroxymethyl) phosphoni-um chloride, the resulting product has a purity of about ninety-six point five percent. In contrast, when phosphine prepared Vin accordance with the Vinstant novel process -is used to prepare tetrakis(hydroxymethyl) phosphonium chloride, the purity of the product is as high as ninety-nine point ninepercent.

An important advantage in preparing phosphine in accordance with the instant novel process, is that the gas is free from other Aphosphorus hydrides, and therefore, is not spontaneously iiammable when in Contact with air.

The following examples are presented to define the invention more clearly Without any intention of being limited thereby. All parts and percentages arerby weight unless otherwise specied.

Commercially acceptable phos- A cell of the design shown in the drawing was used to prepare phosphine. The cell vesel was a two-liter glass beaker, and theV cathode section Vwas a porous alundum cylinder, having an inside diameter of three inches, and a volume of-about seven hundred milliliters. 'llhe porous alundum served as the diaphragm. The anode was a. lead cylinder having an inside diameter of three and fiveeighths inches, and a height of three and one-half inches. The lead cylindrical anode was perforated with oneeighth inch diameter holes.

Thirty-live milliliters of mercury and twenty grams of molten white phosphorus were placed in the cathode section. About sixteen hundred milliliters of aqueous eighteen percent phosphoric acid `were added to the cathode and anode sections. A current of 2.1 amperes and a voltage of seven volts were impressed upon the system during the electrolysis. No stirring of the molten phosphorus and mercury was employed in this test. 'I'he temperature of the molten phosphorus and electrolyte was maintained at about seventy-seven degrees centigrade. A gaseous mixture of phosphine and hydrogen, having a concentration of twenty percent phosphine byvolume was produced at the cathode at the rate of 13.5 milliliters per minute. Y

Example 2 The procedure of Example l, employing the cell of Example 1, was repeated with the exceptions noted hereinafter. |Fifty milliliters of mercury and thirty-live grams of molten white phosphorus Awere added to the cathode section. An aqueous forty percent phosphoric acid solution lwas employed as the electrolyte. A current of live amperes and a Voltage of 5.3 volts were impressed on the system during electrolysis. The temperature of the electrolyte and molten phosphorus were maintained at a temperature about eighty-rive degrees centigrade, by placing the cell vessel in a constant temperature bath.

The liquids `in the cathode chamber were vigorously agitated during electrolysis, so that t-he mercury cathode contacted the electrolyte as well as the molten phosphorus.

A gaseous mixture of hydrogen and phosphine was produced at the cathode at the ,rate of 2.6.2 milliliters per minute `and had a phosphine concentration of 85.5 percent by volume.

Y Example 3 The procedure of Example 2 was repeated with the exceptions noted hereinafter. The anode was the lead cylinder employed in Example 2, having a three-eighths inch "graphite rod connected thereto. `Fifty milliliters of mercury and thirty grams of molten phosphorus Were added to the cathode section. A current of two amperes and a voltage of four volts were impressed on the system during the electrolysis.

A gaseous mixtune of phosphine and hydrogen was produced at the cathode at the rate of 10.5V milliliters per minute, and had a phosphine concentration of 83.5 percent by volume.

Example 4 linch thick and about three inches in diameter was placedV in the bottomof the cell vessel, and thirty grams of mol ten white phosphorus were added thereto. No agitation was proyided in the anode section, but agitation in the cathode section was effected by means of a magnetic stirrer.

The electrolyte and molten phosphorus were heated to a temperature of eighty-tive degrees centigrade, whereby the metal disk melted. A copper wire was inserted into the bottom of the cathode section to contact the liquidv metal cathode and connect it with the source of direct current.

A current of one ampere and a voltage of seven volts was impressed upon the system during electrolysis. The temperature of the electrolyte, molten phosphorus and liquid lalloy cathode was maintained at eight-,tive degrees centigrade during electrolysis by means of a constant temperature bath.

The gaseous mixture of phosphine `and hydrogen produced at the cathode had a concentration of 92.5 percent pbosphine by volume, and was produced at the rate of 7.3 milliliters per minute.

Example 5 The procedure of Example 4 was repeated, employing the cell of Example 4, with the exceptions noted hereinafter. Fifty milliliters of mercury were added to the cathode section of the cell vessel to serve as 1a cathode instead of the Woods metal. A current of one-half ampere and a voltage of eight vol-ts were impressed upon the system dur-ing electrolysis. A temperature of ninety degrees centigrade was maintained in the cathode section.

The gaseous mixture of phosphine Eand hydrogen produced `at the cathode contained ninety-tive percent phosphine by volume and was produced at the rate of 2.7 milliliters per minute.

It will be recognized by those skilled in the art that Various modications within the invention are possible, some of which have been referred to above. Therefore, I do not wish to be limited except as defined by the appended claims.

I claim:

l. 'Ehe process for the production of phosphine which comprises passing an electric current between an anode 4and a liquid cathode in contact with yan aqueous electrolyte to yield a cathodic current density of Aat least about tive amperes per square foot, said cathode being in contact with molten phosphorus, whereby phosphine is produced at the cathode.

2. The process of claim 1 wherein said cathode is in agitated 'contact with said molten phosphorus.

3. The process of claim 1 wherein said cathode is mercury.

4. The process of claim 1 wherein said cathode is a liquid alloy of bismuth, lead, tin and cadmium.

5. The process of claim 1 wherein said electrolyte is capable of forming hydrogen ions under the electrolysis conditions employed and is non-reactive with molten phosphorus.

6. The process of claim 1 wherein said electrolyte is phosphoric acid.

7. The process of claim 1 wherein said electrolyte is an aqueous phosphoric acid solution containing between about ten 'and about eighty percent phosphoric acid by weight.

8. The process of claim 1 wherein the temperature of the electrolyte and molten phosphorus is maintained during electrolysis within the range between about forty-four and labout .two hundred and eighty degree centigrade 9. The process iof claim 1 wherein the temperature of the electrolyte and molten phosphorus is maintained during electrolysis within the range between about iifty and about one hundred and twenty degrees centigrade.

10. The process of claim 1 wherein the current density of said cathode during electrolysis is maintained in the range between about ten and about seven hundred amperes per square foot.

11. The process of claim 10 wherein the voltage during electrolysis is maintained below .about twenty volts.

12. The process for preparing phosphine which comprises passing an electric current between `an anode and a mercury cathode in contact with an aqueous phosphoric acid solution electrolyte, a portion of said electrolyte in Contact with said mercury cathode being admixed with molten phosphorus, said molten phosphorus being in agitated contact with said cathode, and maintaining a current density on said mercury cathode of at least about tive amperes per 4square foot, whereby `a phosphine-containing gas is produced at the cathode.

References Cited iu the tile of this patent OTHER REFERENCES Ephraim: Inorganic Chemistry, 5th ed. (1948), pages 617-622.

Pauling: College Chemistry, 1955, pages S30-335.

Journal Aof Chemical Society, volume `16 (1863), pages 263-272.

Treatise on Powder Metallurgy, by Goetzel, volume III, 1952, page 63 (#907), 

1. THE PROCESS FOR THE PRODUCTION OF PHOSPHINE WHICH COMPRISES PASSING AN ELECTRIC CURRENT BETWEEN AN ANODE AND A LIQUID CATHODE IN CONTACT WITH AN AQUEOUS ELECTROLYTE TO YIELD A CATHODIC CURRENT DENSITY OF AT LEAST ABOUT FIVE AMPERES PER SQUARE FOOT, SAID CATHODE BEING IN CONTACT WITH MOLTEN PHOSPHORUS, WHEREBY PHOSPHINE IS PRODUCED AT THE CATHODE. 